classes connection

I downloaded project from https://vaadin.com/docs/latest/guide/quick-start
Can anyone explain, how does it run, if my classes are not connected to each other ?
i mean in both classes i cannot see any mentions of other class
image.png

Sounds like your first application. You should really read up about the used software - here for example spring boot as underlying container that handles Inversion of Control, Dependency Injection and other stuff so you don’t have wire anything manually.

i could not find explanation

https://www.baeldung.com/inversion-control-and-dependency-injection-in-spring

In the background Vaadin takes care to registry the routes they have found by scanning your app.

Thank you